Safety device for elevators and similar transporting means



' May-14, 1957 1-, FREDH ETAL 2,792,106

SAFETY DEVICE FOR ELEVATORS AND SIMILAR TRANSPOR'iING MEANS Filed Sept.13, 1954 Fig.1,

United States Patent SAFETY DEVICE FOR ELEVATORS. TRANSPORTINQME'ANSTore Fredh, Stockholm, and Evert lil li arkemjohannes- I hov, Stockholm,Sweden, assigno'i's to Aktiebolaget Svenska Flaktfabriken, Stockholm,Sweden The present invention relates to a safety device for I elevatorsand similar transporting means provided with a driving device andequipped with magnetically conductive receptacles for the material to beconveyed or other regularly spaced parts of iron or the like.

In elevators and similar conveyQts-Where belts transport the material orcarry a plurality of receptacles, for instance elevator buckets, thebelt often tends to slip on the driving drum if overloaded or ifinterfering objects happen to come into the space between the conveyorand its casing. often the case as the elevators usually-are'rathe'r highand extend through several floors in for instance a magazinebuilding-the slipping is allowed to continue for some time, thisresulting in considerable disadvantageous re- 'sults: the belts are wornout quickly and there is a tremendous risk of fire caused by frictionbetween the driving drum and the belt. This risk is especially seriousif the material to be transported consists of grain or other inflammablematerial.

A primary object of the invention is to provide an electromagneticsafety device for eliminating these disadvantages by disconnecting thecurrent to the driving motor of the elevator or stopping the elevator bymechanically disconnecting the conveyor from the driving means, whenslipping occurs.

The present invention is mainly characterized by electric currentinducing means mounted adjacent to the belt conveyor and consisting of apermanent magnet and a coil wound around an iron core, which coil viarectifying means and preferably an electronic amplifier is connectedwith a sensitive relay responsive to the voltage generated in accordancewith changes in the current occurring when the buckets pass the inducingmeans, the core arm of said relay being arranged to disconnect to thedriving motor of the conveyor or to actuate a device for mechanicallydisconnecting the conveyor from the driving means as well as to energizesimultaneously an alarm system if the intervals between the changes incurrent exceed a predetermined value. The inducing means may suitably beenclosed in a shell of iron for directing the magnetic field of saidmeans towards the conveyor.

A suitable modification within the scope of the invention is theaddition of means for the adjusting of the response of the relay toditferent values of the intervals between the changes in the current.

The invention will now be described more in detail with reference to theaccompanying drawings in which,

Fig. 1 illustrates one embodiment of an electromagnetic safety device inaccordance with the invention; and

Fig. 2 illustrates a second embodiment of the present invention.

In the embodiments illustrated in the drawings, the elevator is equippedwith iron buckets for transporting the material, for instance grain .orsimilar material. The invention may, however, also be used in other beltconveyors, if the belt is provided with any regularly spaced If suchslipping is not observed-which is 2,792,106 Patented May 14, 1957 ice 2iron parts. Bolts, jointing irons or other iron parts may thus beattached to the belt for operating the safety device.

In the drawings, reference number 1 designates a coil arranged on aniron core 2, of a permanent magnet 2a, which together constitute anelectric current inducing means 20. The permanent magnet 2a is alignedwith the core at the rear end, and the assembly is provided with an ironshell 5. The function of this shell is to direct the magnetic fieldtowards the coil and towards the path of the belt 17 driven by a pulley16 and carrying buckets 18. In the illustrated embodiments, as thebuckets 18 move past the iron core 2, a change of the electromagneticfield results, and an alternating current is induced in the coil 1. Thiscurrent is rectified by means of rectifying means 4 for instance diodesof germanium. v The rectified current energizes in the embodimentillustrated in Fig. l, a polarized relay 6, the contacts of whichcontrol a motor relay connected between the electric source 12a and anelectric motor 13 for the elevator belt or belts. An electronicamplifier may be provided between the rectifying means 4 and the motorrelay 12.

The device may also be arranged as shown in Fig. 2 wherein the relay 6controls a solenoid 14 of a clutch 15 for mechanically disconnecting anelectric motor driving the elevator belts. The remaining elements of thecircuitare identical to those shown in Fig. 1 and have beengivenidentical reference numerals.

Reference number 11 in each figure designates an alarm bell responsiveto the relays 6, 8, when the degree of slipping has reached apredetermined extent. Reference number 7 designates a condensor orcapacitor shunted across the coil of the relay 6. By means of such acondensor an adjustment of the sensitivity of the relay can be made.Furthermore there are in the illustrated forms of the safety device arelay 8, a switch 9 and a transformer 10, all of designs prior known.

Within the scope of the invention is an apparatus having twin elevators,as shown in Fig. 1, there is inducing means 20 and 20a for each of thebelts 17 and 17a. The two inducing means 20 and 20a are connected inseries and are connected by the responsive relay 6 to the motor relay12.

In the operation of the safety device the advance of the iron parts 18of the conveyor past the current inducing means 20 creates a surge ofcurrent in the coil 1. The

I current is rectified by the rectifier 4 to provide a positiveoperating normally, the relay 6 is maintained energized constantly,whereas if the conveyor slows below a minimum speed, the capacitor 7fails to maintain the relay energized, and causes its contacts to open.

When the relay 6 is energized, the contacts of the relay 6 energize therelay 8 which completes a circuit to either the relay 12 of Fig. l, orthe electric actuator or solenoid 14 of the clutch 15 of Fig. 2. Whenthe relay 6 is deenergized, the opening of the contacts of the relaydeenergizes the relay 8, opening the circuit to the relay 12' or theclutch 14 and closing a circuit to the alarm bell 11. The push buttonswitch 3 is provided to by-pass thelower contacts of the relay 8 toenergize either the relay 12 or the electric clutch 14 for manualoperation of theconveyor. Thus, when the conveyor is operating at orabove the desired speed, the drive means for the conveyor is renderedoperable, and when the speed of the conveyor falls below the desiredspeed, the drive means is rendered inoperable and an alarm is energized.

To adjust the safety device to be responsive to diiferent rates ofadvance of the belt 17, the capacitor 7 is ad justed. A meter M isprovided to indicate the frequency of the current changes induced by theinducing means 20, thereby indicating the operation of the conveyor 17.

It is to be understood that the clutch 14, 15 of Fig. 2 may be employedwith twin conveyors, as shown in Fig. l, and the relay 12 of Fig. 1 maybe employed with a single conveyor as shown in Fig. 2. Thus whilespecific embodiments of the present invention have been hereinillustrated and described, changes and modifications may be made withinthe scope of the following claims.

What is claimed is:

1. For elevators and similar endless conveyors provided withmagnetically conductive receptacles for the material to be conveyed orother regularly interspaced parts of iron, said conveyor havingselectively operable drive means, .a safety device characterized by anelectric current inducing means mounted adjacent said conveyor andconsisting of a permanent magnet, an iron core disposed between saidmagnet and said conveyor, and .a coil wound around said core, saidcurrent inducing means being operable upon advance of each of said partsof iron past said current-inducing means to generate a surge of currentin said coil, circuit means including a sensitive relay electricallyconnected to said coil and energized by said surges, means in saidcircuit means maintaining said relay energized for a predeterminedinterval after each surge, a second circuit means including contacts ofsaid relay and operable upon enrgization of said relay to maintain saiddrive means operative.

2. A safety device according to claim 1 wherein said selectivelyoperable drive means comprises an electric motor and said second circuitmeans includes a relay actuatable to connect said motor to a source ofcurrent.

3. A safety device according to. claim 1 wherein selectively operabledrive means comprises an electrically actuated clutch, and whereinfurther said second circuit means includes an actuator for said clutchactuatable to engage said clutch.

4. A safety device according to claim 1 including an alarm system insaid second circuit energized upon deenergization of said relay togenerate an alarm signal. I

5. A device according to claim 1 wherein said current inducing meansincludes a shell of iron surrounding said magnet and said core to directthe magnetic field of said magnet toward said conveyor.

6. A device according to claim 1 wherein said means for maintaining saidrelay energized for a predetermined interval is adjustable to changesaid predetermined intcrval.

7. A device according to claim 1 for a plurality of conveyors driven bysaid drive means including a current inducing means for each of saidconveyors, said plurality of current inducing means being connected inseries in said first circuit means to energize said relay. Y

8. A device according to claim 1 including meter means in said firstcircuit means responsive to the fro quency of said surges of current tothereby indicate the speed of operation of the conveyor.

References Cited in the file of this patent UNITED STATES PATENTS2,503,812 Fath Apr. 11, 1950

